How can I do the summatory of elements in a list of lists in python?

Question

Possible Duplicate:
sum each value in a list of tuples

I need help with this problem, Thank you in advance for your colaboration. I would like obtein this:

result=[12,15,18]

from

a= [[1,2,3],[4,5,6],[7,8,9]]

I am trying with the code below that works, but I would like find a general form for to do this in the case the internal lists could be variables.

lista=[[5, 7, 9], [8, 11, 13], [11, 13, 15]]

b2 = [lista [0][i]+ lista [1][i] + lista [2][i] for i in range(len(lista))]

print (b2)

Thank you very much.

Thank you very much Ashwini Chaudhary, the question was duplicated, this explication works perfect, very kind of you part. — user1965825, Jan 10 '13 at 07:48
Heck, list comprehension works too, but is a bit convoluted. `[sum((a[i][j] for i in xrange(len(a)))) for j in xrange(len(a[0]))]` — Snakes and Coffee, Jan 10 '13 at 08:04

score 2 · Answer 1 · answered Jan 10 '13 at 07:45

2

a= [[1,2,3],[4,5,6],[7,8,9]]
result = map(sum, zip(*a))
print result

answered Jan 10 '13 at 07:45

Jun HU

complementing the helpful answer of Jun HU in python 3 could be: lista=[[1,2,3],[4,5,6],[7,8,9]] g=[] for i in map(sum, zip(*lista)): g.append(i) print (g) Thanks, – user1965825 Jan 10 '13 at 08:40

score 0 · Accepted Answer · answered Jan 10 '13 at 07:46

0

I would do it this way:

# a is some list
b2 = [0]*len(a[0])
for x in a:
    for y in range(len(x)):
         b2[y] += x[y]
print(b2)

answered Jan 10 '13 at 07:46

Abs

This is very un-pythonic compared to `zip()` based solution. – Ashwini Chaudhary Jan 10 '13 at 07:58

2 Answers2